Every household that considers rooftop solar eventually asks the same question: "Would my money earn more in a bank fixed deposit?" It is a reasonable question. Fixed deposits are familiar, safe, and require zero effort after opening. Solar requires an upfront investment, sits on your roof, and involves a technology most people do not fully understand. But when you run the actual numbers -- factoring in tax treatment, inflation, electricity tariff escalation, and the 25-year productive life of a solar system -- the comparison is not even close.

This analysis compares a Rs 2,12,000 rooftop solar investment (a 3 kW system after PM Surya Ghar subsidy in Tamil Nadu) against placing the same amount in a bank fixed deposit. We use real 2026 numbers, not theoretical projections.

The Two Investments Side by Side

Investment A: 3 kW Rooftop Solar System

Gross cost: Rs 1,90,000
PM Surya Ghar subsidy: Rs 78,000
Net investment: Rs 1,12,000
Location: Tamil Nadu (average 4.2 units/kW/day generation)
Current electricity tariff: Rs 4.00-5.50/unit (TANGEDCO domestic slab for 400-800 units bi-monthly consumption)
Annual generation: Approximately 4,600 units (declining 0.5% per year)
Maintenance cost: Rs 3,000-5,000/year

Investment B: Bank Fixed Deposit

Principal: Rs 1,12,000 (same as net solar investment)
Interest rate: 7.0% per annum (2026 average for 5-year SBI FD)
Tax treatment: Interest taxable at slab rate
Tenure: We will track both investments over 10 and 25 years

Year-by-Year Comparison: First 10 Years

Solar Returns

Solar "returns" come as electricity bill savings -- money you do not have to pay TANGEDCO. These savings are completely tax-free for residential consumers.

Year	Annual Generation (units)	Effective Tariff (Rs/unit)	Annual Savings	Maintenance Cost	Net Annual Benefit	Cumulative Benefit
1	4,600	4.50	20,700	3,000	17,700	17,700
2	4,577	4.68	21,420	3,000	18,420	36,120
3	4,554	4.87	22,178	3,500	18,678	54,798
4	4,531	5.06	22,927	3,500	19,427	74,225
5	4,508	5.26	23,712	3,500	20,212	94,437
6	4,486	5.47	24,538	4,000	20,538	1,14,975
7	4,463	5.69	25,394	4,000	21,394	1,36,369
8	4,441	5.92	26,291	4,000	22,291	1,58,660
9	4,419	6.16	27,221	4,500	22,721	1,81,381
10	4,397	6.41	28,184	4,500	23,684	2,05,065

Assumptions: 0.5% annual panel degradation, 4% annual TANGEDCO tariff increase (conservative -- historical average is 5-7%), blended effective tariff starting at Rs 4.50/unit.

Fixed Deposit Returns

Year	Opening Balance	Interest Earned (7%)	Tax on Interest (30% slab)	Net Interest	Cumulative Net Return
1	1,12,000	7,840	2,352	5,488	5,488
2	1,17,488	8,224	2,467	5,757	11,245
3	1,23,245	8,627	2,588	6,039	17,284
4	1,29,284	9,050	2,715	6,335	23,619
5	1,35,619	9,493	2,848	6,645	30,264
6	1,42,264	9,958	2,987	6,971	37,235
7	1,49,235	10,446	3,134	7,312	44,547
8	1,56,547	10,958	3,287	7,671	52,218
9	1,64,218	11,495	3,449	8,046	60,264
10	1,72,264	12,058	3,617	8,441	68,705

Assumptions: 7% FD rate sustained (rates may fall), reinvestment at same rate, 30% tax slab (new tax regime). If you are in the 20% slab, FD returns improve slightly but the gap remains large.

10-Year Summary

Metric	Solar	Fixed Deposit
Initial investment	Rs 1,12,000	Rs 1,12,000
Cumulative returns (10 years)	Rs 2,05,065	Rs 68,705
Effective annual return (IRR)	18-22%	4.9% (post-tax)
Tax paid on returns	Rs 0	Rs 29,444
Asset remaining	Solar system (15+ years life left)	Rs 0 (FD matured)

Solar delivers approximately 3x the returns of a fixed deposit over 10 years.

The 25-Year Picture

Solar panels are warranted for 25 years with guaranteed output above 80% of rated capacity. The inverter typically needs one replacement around year 12-15 (cost: Rs 25,000-40,000 for a 3 kW string inverter).

Metric	Solar (25 years)	Fixed Deposit (25 years)
Cumulative savings/returns	Rs 9,50,000 - 12,00,000	Rs 3,20,000 - 3,80,000
Inverter replacement cost	Rs 35,000	N/A
Total maintenance cost	Rs 1,00,000 - 1,25,000	Rs 0
Net cumulative benefit	Rs 8,25,000 - 10,75,000	Rs 3,20,000 - 3,80,000
Tax paid	Rs 0	Rs 1,40,000 - 1,65,000

Over 25 years, the solar investment returns Rs 8-10 lakh net on a Rs 1.12 lakh investment. The same amount in an FD returns Rs 3.2-3.8 lakh before the erosion of purchasing power by inflation.

What About Inflation?

This is where solar truly dominates. Fixed deposit interest rates historically track close to inflation (6-7% FD rate vs 5-6% inflation), meaning real returns are 1-2% at best, and often negative after tax. Your FD corpus grows in nominal terms but buys roughly the same amount of goods 10 years later.

Solar savings, by contrast, increase with inflation because electricity tariffs rise over time. Every rupee of tariff increase directly increases your annual solar savings. Your solar system is, in effect, an inflation-hedged asset that becomes more valuable as prices rise.

Risk Comparison

Risk Factor	Solar	Fixed Deposit
Capital safety	Hardware on your roof; insurable	Bank guarantee up to Rs 5 lakh (DICGC)
Returns certainty	Highly predictable (sun is reliable)	Rate changes at renewal
Inflation protection	Built-in (rising tariffs = rising savings)	None (fixed nominal returns)
Liquidity	Cannot be withdrawn; savings are monthly	Premature withdrawal with penalty
Technology risk	Panels last 25+ years; mature technology	None
Counterparty risk	You own the asset	Bank solvency (low risk)

Solar carries slightly higher complexity risk (you need a good installer, proper maintenance, and functioning net metering), but the financial rewards overwhelmingly compensate. The key risk mitigator is choosing an experienced, MNRE-empanelled installer who handles the TANGEDCO process and provides long-term maintenance support.

When an FD Might Still Make Sense

To be fair, there are situations where a fixed deposit is the better choice:

You do not own the property (rented home -- you cannot install solar)
Your roof is unsuitable (heavy shading, structural issues, north-facing with no alternatives)
Your electricity consumption is very low (under 100 units bi-monthly -- you are already in the free slab)
You need liquidity within 2-3 years (solar payback takes 4-6 years)
You are planning to sell the property within 3-4 years (though solar increases property value by 3-5%)

For everyone else -- especially Tamil Nadu homeowners paying Rs 4+ per unit -- the solar investment case is overwhelming.

The Verdict

A rooftop solar system in Tamil Nadu is not just a green choice -- it is the single best fixed-income-equivalent investment available to a homeowner in 2026. It delivers 18-22% effective IRR (compared to 4.9% post-tax FD returns), provides complete inflation protection, and continues generating returns for 25 years with minimal maintenance.

The question is not whether solar beats an FD. It does, conclusively. The question is how quickly you can get your system installed and start saving.

Use our solar savings calculator to see the exact comparison for your electricity consumption level, or contact Tristar for a personalised financial analysis based on your TANGEDCO bill.

Solar Investment vs Fixed Deposit: Which Gives Better Returns in 2026?